English
An element g of a group acting on a Type is regular.
Русский
Элемент группы G, действующий на множество, является регулярен.
LaTeX
$$$IsSMulRegular M g$ for any g ∈ G with group structure$$
Lean4
/-- An element of a group acting on a Type is regular. This relies on the availability
of the inverse given by groups, since there is no `LeftCancelSMul` typeclass. -/
theorem isSMulRegular_of_group [MulAction G R] (g : G) : IsSMulRegular R g :=
by
intro x y h
convert congr_arg (g⁻¹ • ·) h using 1 <;> simp [← smul_assoc]